I tested 3G performance on the iPhone 4 twice (three runs each) — once lying on a table, and once while held in my left hand, with my palm spanning the infamous lower-left antenna gap. I also tested it using my home 802.11n Wi-Fi network, connected to a Comcast cable modem.

So I’m seeing download speeds twice as fast as on an iPhone 3GS, and upload speeds over ten times faster. Latency is about an order of magnitude better as well. The iPad doesn’t fare much better than the 3GS.

Holding the iPhone 4 in my hand drops the 3G download speed by about a third, but it’s still faster than the 3GS. Upload speed and latency didn’t seem affected by holding it in my hand.